Liquid-cooled heat sink configured to facilitate drainage

ABSTRACT

Cooling apparatuses, cooled electronic modules, and methods of fabrication are provided which facilitate heat transfer from one or more electronic components to a liquid coolant in an operational mode, and drainage of coolant therefrom in a transport mode. The cooling apparatus includes a liquid-cooled heat sink configured to horizontally couple along a main heat transfer surface to the electronic component(s). The heat sink includes a thermally conductive structure with a coolant-carrying compartment through which coolant flows, and a coolant inlet tube and a coolant outlet tube affixed to the thermally conductive structure and in fluid communication with the coolant-carrying compartment to facilitate coolant flow through the compartment. The coolant-carrying compartment has a base surface, and the coolant outlet tube extends into the coolant-carrying compartment towards the base surface to facilitate withdrawal of the liquid coolant from the compartment in the transport mode of the cooling apparatus.

BACKGROUND

As is known, operating electronic components produce heat. This heatshould be removed in an effective manner to maintain device junctiontemperatures within desirable limits, with failure to do so resulting inexcessive component temperatures, potentially leading to thermal runawayconditions. Several trends in the electronics industry have combined toincrease the importance of thermal management, including heat removalfor electronic components, including technologies where thermalmanagement has traditionally been less of a concern, such as CMOS. Inparticular, the need for faster and more densely packed circuits has hada direct impact on the importance of thermal management. First, powerdissipation, and therefore heat production, increases as deviceoperating frequencies increase. Second, increased operating frequenciesmay be possible at lower device junction temperatures. Further, as moreand more devices or components are packed onto a single chip, heat flux(Watts/cm²) increases, resulting in the need to dissipate more powerfrom a given size chip or module. These trends have combined to createapplications where it is no longer desirable to remove heat from moderndevices solely by traditional air cooling methods, such as by using aircooled heat sinks with heat pipes or vapor chambers. Such air coolingtechniques are inherently limited in their ability to extract heat froman electronic component with high power density.

The need to cool current and future high heat load, high heat fluxelectronic devices therefore mandates the development of aggressivethermal management techniques using, for instance, liquid cooling.

BRIEF SUMMARY

In one aspect, provided herein is a cooling apparatus comprising aliquid-cooled heat sink. The liquid-cooled heat sink includes: athermally conductive structure configured to couple along a horizontalmain heat transfer surface thereof to at least one electronic componentto be cooled, the thermally conductive structure including acoolant-carrying compartment through which liquid coolant flows, atleast in part, in a direction substantially parallel to the main heattransfer surface of the thermally conductive structure; a coolant inlettube and a coolant outlet tube associated with the thermally conductivestructure and in fluid communication with the coolant-carryingcompartment of the thermally conductive structure to facilitate theliquid coolant flow therethrough; and wherein the coolant-carryingcompartment of the thermally conductive structure comprises a basesurface, and the coolant outlet tube extends into the coolant-carryingcompartment towards the base surface thereof to facilitate withdrawal ofthe liquid coolant therefrom for a transport mode of the coolingapparatus.

In another aspect, a cooled electronic module is provided which includesat least one electronic component, and a cooling apparatus to facilitatecooling the at least one electronic component. The cooling apparatusincludes a liquid-cooled heat sink horizontally coupled to the at leastone electronic component to be cooled. The liquid-cooled heat sinkcomprises: a thermally conductive structure with a coolant-carryingcompartment through which coolant flows, at least in part, in adirection substantially parallel to the horizontal main heat transfersurface of the liquid-cooled heat sink; and a coolant inlet tube and acoolant outlet tube associated with the thermally conductive structureand in fluid communication with the coolant-carrying compartment of thethermally conductive structure to facilitate the liquid coolant flowtherethrough. The coolant-carrying compartment of the thermallyconductive structure further includes a base surface, and the coolantoutlet tube extends into the coolant-carrying compartment towards thebase surface thereof to facilitate withdrawal of the liquid coolanttherefrom for a transport mode of the cooled electronic module.

In a further aspect, a method is provided which includes providing acooling apparatus comprising a liquid-cooled heat sink configured tofacilitate cooling at least one electronic component, the coolingapparatus having an operational mode and a transport mode. Theliquid-cooled heat sink includes: a thermally conductive structureconfigured to couple along a horizontal main heat transfer surfacethereof to the at least one electronic component to be cooled, thethermally conductive structure including a coolant-carrying compartmentthrough which liquid coolant flows, at least in part, in a directionsubstantially parallel to the horizontal main heat transfer surface ofthe thermally conductive structure; a coolant inlet tube and a coolantoutlet tube associated with the thermally conductive structure and influid communication with the coolant-carrying compartment of thethermally conductive structure to facilitate the liquid coolant flowtherethrough; and wherein the coolant-carrying compartment of thethermally conductive structure comprises a base surface, and a coolantoutlet tube extends into the coolant-carrying compartment towards thebase surface thereof to facilitate withdrawal of the liquid coolanttherefrom in the transport mode of the cooling apparatus.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more aspects of the present invention are particularly pointedout and distinctly claimed as examples in the claims at the conclusionof the specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts one embodiment of a liquid-cooled data center comprisinga coolant distribution unit which facilitates liquid-cooling ofelectronics racks of the data center, in accordance with one or moreaspects of the present invention;

FIG. 2 is a plan view of one embodiment of an electronic system (ornode) layout illustrating an air and liquid cooling apparatus forcooling components of the electronic system, in accordance with one ormore aspects of the present invention;

FIG. 3 depicts one detailed embodiment of a partially assembledelectronic system layout, wherein the electronic system includes eightheat-generating electronic components to be cooled, each having, in oneembodiment, a respective cooling apparatus associated therewith, inaccordance with one or more aspects of the present invention;

FIG. 4A depicts one embodiment of a cooled electronic module comprisingat least one electronic component and a cooling apparatus comprising aliquid-cooled heat sink, in accordance with one or more aspects of thepresent invention;

FIG. 4B depicts a cross-sectional elevational view of one embodiment ofthe liquid-cooled heat sink of FIG. 4A, taken through the coolant inletand outlet tubes, in accordance with one or more aspects of the presentinvention;

FIG. 4C depicts the liquid-cooled heat sink of FIG. 4B, with the coolingapparatus in a transport mode, and showing liquid coolant partiallydrained from the coolant-carrying compartment of the heat sink, inaccordance with one or more aspects of the present invention;

FIG. 5 is a schematic of one embodiment of a coolant-servicingapparatus, which may be employed in transitioning the cooling apparatusdisclosed herein between operational and transport modes, in accordancewith one or more aspects of the present invention;

FIG. 6A is a cross-sectional elevational view of an alternate embodimentof a liquid-cooled heat sink such as depicted in FIG. 4A, taken throughthe coolant inlet and outlet tubes thereof, and illustrating an extendedcoolant outlet tube reaching further into the coolant-carryingcompartment of the heat sink, in accordance with one or more aspects ofthe present invention;

FIG. 6B depicts an alternate embodiment of the liquid-cooled heat sinkof FIG. 6A, in accordance with one or more aspects of the presentinvention; and

FIG. 6C depicts another embodiment of the liquid-cooled heat sink ofFIGS. 6A & 6B, in accordance with one or more aspects of the presentinvention.

DETAILED DESCRIPTION

As used herein, the terms “electronics rack” and “rack unit” are usedinterchangeably, and unless otherwise specified include any housing,frame, rack, compartment, blade server system, etc., having one or moreheat-generating components of a computer system, electronic system, orinformation technology equipment, and may be, for example, a stand-alonecomputer processor having high, mid or low end processing capability. Inone embodiment, an electronics rack may comprise a portion of anelectronic system, a single electronic system, or multiple electronicsystems, for example, in one or more sub-housings, blades, books,drawers, nodes, compartments, etc., having one or more heat-generatingelectronic components disposed therein. An electronic system within anelectronics rack may be movable or fixed relative to the electronicsrack, with rack-mounted electronic drawers being an example of systemsof an electronics rack to be cooled.

“Electronic component” refers to any heat-generating electroniccomponent of, for example, a computer system or other electronics unitrequiring cooling. By way of example, an electronic component maycomprise one or more integrated circuit die (or chips) and/or otherelectronic devices to be cooled, including one or more processor chips,memory chips and/or memory support chips. Further, the term “cold plate”refers to any thermally conductive structure having one or morecompartments, channels, passageways, etc., formed therein for flowing ofcoolant therethrough.

As used herein, a “liquid-to-liquid heat exchanger” may comprise, forexample, two or more coolant flow paths, formed of thermally conductivetubing (such as copper or other tubing) in thermal or mechanical contactwith each other. Size, configuration and construction of theliquid-to-liquid heat exchanger can vary without departing from thescope of the invention disclosed herein. Further, “data center” refersto a computer installation containing one or more electronics racks tobe cooled. As a specific example, a data center may include one or morerows of rack-mounted computing units, such as server units.

One example of the coolants discussed herein, such as the facilitycoolant or system coolant, is water. However, the cooling conceptsdisclosed herein are readily adapted to use with other types of coolanton the facility side and/or on the system side. For example, one or moreof the coolants may comprise a brine, a fluorocarbon liquid, ahydrofluoroether liquid, a liquid metal, or other similar coolant, orrefrigerant, while still maintaining the advantages and unique featuresof the present invention.

Reference is made below to the drawings, which are not drawn to scale tofacilitate an understanding thereof, wherein the same reference numbersused throughout different figures designate the same or similarcomponents.

In one embodiment, an air-cooled data center may have a raised floorlayout, where multiple electronics racks are disposed in one or morerows. Such a data center may house several hundred, or even severalthousand microprocessors. In one implementation, chilled air enters thecomputer room via perforated floor tiles from a supply air plenumdefined between the raised floor and a base or sub-floor of the room.Cooled air is taken in through louvered covers at air inlet sides of theelectronics racks and expelled through the back (i.e., air outlet sides)of the electronics racks. Each electronics rack may have one or more airmoving devices (e.g., fans or blowers) to provide forced inlet-to-outletairflow to cool the electronic devices within the system(s) of the rack.The supply air plenum provides conditioned and cooled air to theair-inlet sides of the electronics racks via perforated floor tilesdisposed in a “cold” aisle of the computer installation. The conditionedand cooled air is supplied to the under-floor plenum by one or more airconditioning units, also disposed within the data center. Room air istaken into each air conditioning unit typically near an upper portionthereof. This room air may comprise in part exhausted air from the “hot”aisles of the computer installation defined, for example, by opposingair outlet sides of the electronics racks.

Due to the ever-increasing airflow requirements through electronicsracks, and the limits of air distribution within the typical data centerinstallation, liquid-based cooling may, for instance, be combined with,or used in place of, the above-described conventional air-cooling. FIGS.1-3 illustrate one embodiment of a data center implementation employinga liquid-based cooling system with one or more cold plates coupled tohigh heat-generating electronic components disposed within anelectronics rack.

In particular, FIG. 1 depicts one embodiment of a data center 101comprising a coolant distribution unit 100. The coolant distributionunit may be a relatively large unit which occupies what would beconsidered a full electronics frame. Within coolant distribution unit100 is a power/control element 112, a reservoir/expansion tank 113, aheat exchanger 114, a pump 115 (possibly accompanied by a redundantsecond pump), facility water inlet 116 and outlet 117 supply pipes, asupply manifold 118 supplying water or system coolant to the electronicsracks 110 via couplings 120 and lines 122, and a return manifold 119receiving water from the electronics racks 110, via lines 123 andcouplings 121. Each electronics rack includes (in one example) apower/control unit 130 for the electronics rack, multiple electronicsystems 140, a system coolant supply manifold 150, and a system coolantreturn manifold 160. As shown, each electronics rack 110 is disposed ona raised floor 165 of the data center 101, with lines 122 providingsystem coolant to system coolant supply manifolds 150 and lines 123facilitating return of system coolant from system coolant returnmanifolds 160 being disposed in the supply air plenum beneath the raisedfloor.

In the embodiment illustrated, the system coolant supply manifold 150provides system coolant to the cooling systems of the electronic systems(such as to liquid-cooled cold plates thereof) via flexible hoseconnections 151, which are disposed between the supply manifold and therespective electronic systems within the rack. Similarly, system coolantreturn manifold 160 is coupled to the electronic systems via flexiblehose connections 161. Quick connect couplings may be employed at theinterface between flexible hoses 151, 161 and the individual electronicsystems. By way of example, these quick connect couplings may comprisevarious types of commercially available couplings, such as thoseavailable from Colder Products Company, of St. Paul, Minn., USA, orParker Hannifin, of Cleveland, Ohio, USA.

Although not shown, electronics rack 110 may also include anair-to-liquid heat exchanger disposed at an air outlet side thereof,which also receives system coolant from the system coolant supplymanifold 150 and returns system coolant to the system coolant returnmanifold 160.

FIG. 2 depicts one embodiment of an electronic system 213 componentlayout wherein one or more air moving devices 211 provide forced airflow 215 to cool multiple components 212 within electronic system 213.Cool air is taken in through a front 231 and exhausted out a back 233 ofthe system. The multiple components to be cooled include multipleprocessor modules to which liquid-cooled heat sinks 220 (of aliquid-based cooling system) are coupled, as well as multiple arrays ofmemory modules 230 (e.g., dual in-line memory modules (DIMMs)) andmultiple rows of memory support modules 232 (e.g., DIMM control modules)to which air-cooled heat sinks are coupled. In the embodimentillustrated, memory modules 230 and the memory support modules 232 arepartially arrayed near front 231 of electronic system 213, and partiallyarrayed near back 233 of electronic system 213. Also, in the embodimentof FIG. 2, memory modules 230 and the memory support modules 232 arecooled by air flow 215 across the electronic system.

The illustrated liquid-based cooling system further includes multiplecoolant-carrying tubes connected to and in fluid communication withliquid-cooled heat sinks 220. The coolant-carrying tubes comprise setsof coolant-carrying tubes, with each set including (for example) acoolant supply tube 240, a bridge tube 241 and a coolant return tube242. In this example, each set of tubes provides liquid coolant to aseries-connected pair of heat sinks 220 (coupled to a pair of processormodules). Coolant flows into a first heat sink of each pair via thecoolant supply tube 240 and from the first heat sink to a second heatsink of the pair via bridge tube or line 241, which may or may not bethermally conductive. From the second heat sink of the pair, coolant isreturned through the respective coolant return tube 242. Note that in analternate implementation, each liquid-cooled heat sink 220 could becoupled directly to a respective coolant supply tube 240 and coolantreturn tube 242, that is, without series connecting two or more of theliquid-cooled heat sinks

FIG. 3 depicts in greater detail an alternate electronic system layoutcomprising eight processor modules, each having a respectiveliquid-cooled cold plate or heat sink of a liquid-based cooling systemcoupled thereto. The liquid-based cooling system is shown to furtherinclude associated coolant-carrying tubes for facilitating passage ofliquid coolant through the liquid-cooled heat sinks and a headersubassembly to facilitate distribution of liquid coolant to and returnof liquid coolant from the liquid-cooled heat sinks By way of specificexample, the liquid coolant passing through the liquid-based coolingsubsystem is cooled and conditioned (e.g., filtered) water.

FIG. 3 is an isometric view of one embodiment of an electronic system ordrawer, and a monolithic cooling system. The depicted planar serverassembly includes a multi-layer printed circuit board to which memoryDIMM sockets and various electronic components to be cooled are attachedboth physically and electrically. In the cooling system depicted, asupply header is provided to distribute liquid coolant from a singleinlet to multiple parallel coolant flow paths and a return headercollects exhausted coolant from the multiple parallel coolant flow pathsinto a single outlet. Each parallel coolant flow path includes one ormore heat sinks in series flow arrangement to facilitate cooling one ormore electronic components to which the heat sinks are mechanically andthermally coupled. The number of parallel paths and the number ofseries-connected liquid-cooled heat sinks depends, for example, on thedesired component temperature, available coolant temperature and coolantflow rate, and the total heat load being dissipated from each electroniccomponent.

More particularly, FIG. 3 depicts a partially assembled electronicsystem 313 and an assembled liquid-based cooling system 315 coupled toprimary heat-generating components (e.g., including processor die) to becooled. In this embodiment, the electronic system is configured for (oras) a node of an electronics rack, and includes, by way of example, asupport substrate or planar board 305, a plurality of memory modulesockets 310 (with the memory modules (e.g., dual in-line memory modules)not shown), multiple rows of memory support modules 332 (each havingcoupled thereto an air-cooled heat sink 334), and multiple processormodules (not shown) disposed below the liquid-cooled heat sinks 320 ofthe liquid-based cooling system 315.

In addition to liquid-cooled heat sinks 320, liquid-based cooling system315 includes multiple coolant-carrying tubes, including coolant supplytubes 340 and coolant return tubes 342 in fluid communication withrespective liquid-cooled heat sinks 320. The coolant-carrying tubes 340,342 are also connected to a header (or manifold) subassembly 350 whichfacilitates distribution of liquid coolant to the coolant supply tubesand return of liquid coolant from the coolant return tubes 342. In thisembodiment, the air-cooled heat sinks 334 coupled to memory supportmodules 332 closer to front 331 of electronic system 313 are shorter inheight than the air-cooled heat sinks 334′ coupled to memory supportmodules 332 near back 333 of electronic system 313. This size differenceis to accommodate the coolant-carrying tubes 340, 342 since, in thisembodiment, the header subassembly 350 is at the front 331 of theelectronics drawer and the multiple liquid-cooled heat sinks 320 are inthe middle of the drawer.

Liquid-based cooling system 315 comprises, in one embodiment, apre-configured monolithic structure which includes multiple(pre-assembled) liquid-cooled heat sinks 320 configured and disposed inspaced relation to engage respective heat-generating electroniccomponents. Each liquid-cooled heat sink 320 includes, in thisembodiment, a liquid coolant inlet and a liquid coolant outlet, as wellas an attachment subassembly (i.e., a cold plate/load arm assembly).Each attachment subassembly is employed to couple its respectiveliquid-cooled heat sink 320 to the associated electronic component toform the cold plate and electronic component (or device) assemblies.Alignment openings (i.e., thru-holes) are provided on the sides of theheat sink to receive alignment pins or positioning dowels during theassembly process. Additionally, connectors (or guide pins) are includedwithin attachment subassembly, which facilitate use of the attachmentassembly.

As shown in FIG. 3, header subassembly 350 includes two liquidmanifolds, i.e., a coolant supply header 352 and a coolant return header354, which in one embodiment, are coupled together via supportingbrackets. In the monolithic cooling structure of FIG. 3, the coolantsupply header 352 is metallurgically bonded in fluid communication toeach coolant supply tube 340, while the coolant return header 354 ismetallurgically bonded in fluid communication to each coolant returntube 352. A single coolant inlet 351 and a single coolant outlet 353extend from the header subassembly for coupling to the electronicsrack's coolant supply and return manifolds (not shown).

FIG. 3 also depicts one embodiment of the pre-configured,coolant-carrying tubes. In addition to coolant supply tubes 340 andcoolant return tubes 342, bridge tubes or lines 341 are provided forcoupling, for example, a liquid coolant outlet of one liquid-cooled heatsink to the liquid coolant inlet of another liquid-cooled heat sink toconnect in series fluid flow the heat sinks, with the pair of heat sinksreceiving and returning liquid coolant via a respective set of coolantsupply and return tubes. In one embodiment, the coolant supply tubes340, bridge tubes 341 and coolant return tubes 342 are eachpre-configured, semi-rigid tubes formed of a thermally conductivematerial, such as copper or aluminum, and the tubes are respectivelybrazed, soldered or welded in a fluid-tight manner to the headersubassembly and/or the liquid-cooled heat sinks The tubes arepre-configured for a particular electronics system to facilitateinstallation of the monolithic structure in engaging relation with theelectronic system.

FIGS. 4A-4B depict in greater detail one embodiment of a cooledelectronic module, generally denoted 400, in accordance with one or moreaspects of the present invention. Referring collectively to FIGS. 4A-4B,cooled electronic module 400 includes one or more electronic components401 to be cooled and a cooling apparatus comprising a liquid-cooled heatsink 410 coupled to the electronic component(s) 401 to facilitatetransfer of heat from the component to, for instance, the liquid coolantpassing through liquid-cooled heat sink 410. In one example, the liquidcoolant may comprises a system coolant distributed such as describedabove in connection with FIGS. 1-3.

Liquid-cooled heat sink 410 includes a thermally conductive structure415, such as a thermally conductive casing or housing, fabricated (forinstance) of a metal, and which includes a coolant-carrying compartment420 (e.g., chamber, channel, tube, passageway, etc.) through whichcoolant flows in a direction 405 through the compartment from a coolantinlet tube 411 to a coolant outlet tube 412 of liquid-cooled heat sink410. In this example, thermally conductive structure 415 includes ahorizontal main heat transfer surface 413 coupled to and in thermalcommunication with the electronic component(s) 401 to facilitate heattransfer from the component(s) to the heat sink, and hence, to theliquid coolant flowing through the heat sink. As one example, main heattransfer surface 413 may comprise the base surface of a liquid-cooledheat sink or cold plate configured as disclosed herein.

By way of further detail, the coolant inlet tube 411, and coolant outlettube 412 may comprise, in one example, separately manufactured tubeswhich are metallurgically bonded to the thermally conductive structure415. These tubes may include circumferential barbs 409 (in oneembodiment) for forming a fluid-tight connection with a coolant hose tofacilitate the flow of liquid coolant through the liquid-cooled heatsink 410. In the embodiment of FIG. 4B, a plurality of thermallyconductive fins 421 are disposed within coolant-carrying compartment 420to extend, for instance, upwards from a base surface 425 thereof. Thethermally conductive fins are provided to facilitate heat transfer fromthe heat sink to the liquid coolant flowing through the coolant-carryingcompartment, and the plurality of thermally conductive fins 421 maycomprise various configurations, including pin fins or plate fins, and,if desired, coolant flow channels of varying cross-section to furtherenhance heat transfer. The coolant inlet tube provides liquid coolant toa coolant inlet manifold region 422 of coolant-carrying compartment 420,and the coolant outlet tube exhausts liquid coolant from a coolantoutlet manifold region 423 of coolant-carrying compartment 420.

As noted briefly above, in one embodiment, the cooling apparatus ofFIGS. 1-4B may have an operational mode, during which liquid coolantflows through the cooling apparatus to facilitate dissipating heat fromone or more electronic components or electronic systems of, forinstance, an electronics rack, and a transport mode, for which asignificant portion of the liquid coolant within the cooling apparatusis removed to reduce or eliminate any damage to the cooling apparatusresulting from freezing during transport. In the embodiment of FIGS.3-4B, the liquid-cooled heat sinks are configured to mount horizontallyto one or more electronic component surfaces to be cooled. Additionally,as illustrated in FIG. 3, the supply and return headers for the liquidcoolant flow may be above the liquid-cooled heat sink(s). Thus,transitioning of the cooling apparatus from an operational mode to atransport mode where it is desired that most of the liquid coolant beremoved from the cooling apparatus, may prove problematic.

As shown in FIG. 4C, in attempting to drain or pump liquid coolant fromthe cooling apparatus, it is possible that a certain volume of coolantwill remain within the coolant-carrying compartment of the heat sink, asillustrated in FIG. 4C. This is particularly likely in the case wherethe liquid-cooled heat sink couples along a horizontal main heattransfer surface to the one or more electronic components to be cooled,with the coolant inlet and outlet tubes being mounted to the heat sinkthrough an upper portion (or surface) of the heat sink, such asillustrated in FIGS. 3-4C. Even in the case where compressed air isemployed to remove liquid coolant from the cooling apparatus, it ispossible that an undesirable amount of liquid coolant may remain withinthe coolant-carrying compartment of a liquid-cooled heat sink positionedand configured as described herein.

FIG. 5 depicts one embodiment of a coolant-servicing apparatus,generally denoted 500, which may be employed in transitioning a coolingapparatus to a transport mode. Coolant servicing apparatus 500 includesa coolant tank 510 and a coolant pump 520 in fluid communication withthe coolant tank for pumping coolant therefrom. Coupled to an output ofcoolant pump 520 are a drain line 525 and multiple parallel-connectedcoolant supply lines 530, 540 & 550 for coupling the coolant pump to acoolant supply port 560 of coolant servicing apparatus 500. Drain line525 includes a coolant control valve S1, which in one embodiment, is asolenoid-operated flow control valve.

Each coolant supply line 530, 540 & 550 of the multipleparallel-connected coolant supply lines also includes asolenoid-operated coolant control valve S2, S3 & S4, respectively, forselectively controlling flow of coolant therethrough pumped by coolantpump 520 from coolant tank 510 to coolant supply port 560. In theembodiment illustrated, coolant supply line 530 further includes adeionization filter 531, and coolant supply line 540 includes aparticulate filter 541, such as a charcoal filter. Coolant supply line550 is a bypass coolant supply line with no filter.

The coolant servicing apparatus 500 further includes a coolant returnport 562. In one embodiment, coolant supply port 560 and coolant returnport 562 are quick connect couplings, which respectively receive asupply line 122 (see FIG. 1) and a return line 123 (FIG. 1) for couplingthe apparatus to the liquid-cooled electronics rack (see FIG. 1). Thequick connect couplings may be any one of various types of commerciallyavailable couplings, such as those available from Colder ProductsCompany, of St. Paul, Minn., USA, or Parker Hannifin, of Cleveland,Ohio, USA.

As illustrated, a first port line 580 couples coolant supply port 560and one end of the multiple parallel-connected coolant supply lines toan upper portion of coolant tank 510 above a coolant full level.Similarly, a second port line 582 couples coolant return port 562 influid communication with an upper portion of coolant tank 510 above acoolant full level thereof. The first port line 580 includes asolenoid-operated coolant control valve S5, while the second port line582 includes a solenoid-operated coolant control valve S7 forcontrolling flow of coolant or air therethrough.

The coolant servicing apparatus further includes a pressurized airsource, which in the embodiment illustrated, comprise an air-compressor570, an air-holding tank 572, an air-regulator 574 and an airflowcontrol valve S6 coupled in-series for provision of pressurized air flowto the coolant supply port 560 of the apparatus for facilitatingdraining of coolant from the cooling system of the liquid-cooledelectronics rack, and for facilitating draining of the coolant servicingapparatus 500 itself. In an alternate embodiment, other pressurized airsources may be employed. For example, the pressurized air source may befacility compressed air, or alternatively, a bottle of compressed gas,such as nitrogen.

If desired, a controller (not shown) can be provided for automatedcontrol of the solenoid-operated control valves to implement theprotocols for filling or draining the cooling apparatuses disclosedherein. Prior to automated operation, a service technician manuallymakes supply line and return line connections to the cooling apparatusor system of the liquid-cooled electronics rack and then, for example,pushes a button or otherwise initiates operation of the coolantservicing apparatus employing a controller programmed with the desiredlogic flows, such as the draining operation described hereinbelow.Alternatively, it is possible to have a fully manual implementation ofthe coolant servicing protocols.

As noted, in one embodiment, liquid coolant may be drained from theapparatus of FIGS. 1-4B employing the coolant-servicing apparatus ofFIG. 5. Liquid-coolant drainage begins by disconnecting system coolantsupply and return lines coupling (for instance) a liquid-cooledelectronics rack to a coolant distribution unit, such as depicted inFIG. 1, and connecting the coolant supply line (e.g., line 122 ofFIG. 1) to the coolant supply port 560 and the coolant return line 123to the coolant return port 562. The coolant tank access cover 512 may beopened, main power is turned ON to the coolant-servicing apparatus, andthe air-compressor 570 is turned ON. Control valve S6 & S7 are opened,allowing air to push through the cooling system and back to the coolanttank. This operation continues for a period time, after which theair-compressor is turned OFF, and control valves S6 & S7 are closed. Themain power to the coolant-servicing apparatus is then turned OFF, andthe coolant tank access cover is closed.

The defined time interval for drainage is selected so most of thecoolant is drained from the cooling system upon expiration of that timeinterval. The amount of time required to drain a particular coolingsystem can be readily determined by experimentation. Draining thecooling system is intended to prepare the liquid-cooled electronics rackfor shipment under conditions which freezing of coolant could occur.This is referred to as the transport mode of the cooling apparatus orelectronics rack. Thus, a sufficient amount of coolant needs to beremoved from each component of the cooling apparatus in critical areasof the system, to preclude the possibility of damage during freezing.The specific time required to achieve this goal depends upon the volumeof the cooling system, the volume of the air-holding tank in theapparatus, and the air regulator discharge pressure. Note that althoughnot relevant to the concepts disclosed herein, the coolant-servicingapparatus 500 of FIG. 5 is also employed in filling the coolingapparatus (or system) during switching from transport mode back to anoperational mode at, for instance, a customer site.

To further assist in drainage of the system coolant from ahorizontally-oriented, liquid-cooled heat sink, such as illustratedabove in connection with FIGS. 4A-4C, variations on the heat sinkstructure are disclosed in FIGS. 6A-6C, and described below. Note thatthe liquid-cooled heat sinks of FIGS. 6A-6C are provided by way ofexample only. Also, unless indicated otherwise, the structures of FIGS.6A-6C are analogous to those described above in connection with FIGS. 4A& 4B.

Referring first to the embodiment of FIG. 6A, the liquid-cooled heatsink 400′ disclosed herein includes a thermally conductive structure 415configured or designed to couple along a horizontal main heat transfersurface 413 thereof to at least one electronic component 401 to becooled. The thermally conductive structure 415 includes acoolant-carrying compartment 420 through which liquid coolant flows, atleast in part, in a direction substantially parallel to the horizontalmain heat transfer surface 413 of thermally conductive structure 415. Acoolant inlet tube 411 and a coolant outlet tube 600 are provided inassociation with the thermally conductive structure 415. For instance,the coolant inlet and outlet tubes could be separately fabricated andmetallurgically bonded (e.g., brazed or welded) to the thermallyconductive structure 415 in a fluid-tight manner, and so as to be influid communication with the coolant-carrying compartment 420 of thethermally conductive structure 415 to facilitate liquid coolant flowtherethrough. In an alternate implementation, the thermally conductivestructure could be fabricated such that the coolant inlet tubes andcoolant outlet tubes are a part of the thermally conductive structure,rather than coupled or affixed to the thermally conductive structure. Ineither case, the inlet and outlet tubes include respectivecoolant-carrying channels or openings through which the liquid coolantflows. The coolant-carrying compartment 420 of the thermally conductivestructure 415 has a base surface 425, and in the embodiment of FIG. 6A,the coolant outlet tube 600 extends into the coolant-carryingcompartment 420 towards base surface 425 thereof to facilitatewithdrawal of any liquid coolant therefrom during a drain operationusing, for instance, a coolant-servicing apparatus such as depicted inFIG. 5. Depending upon the implementation, it may be desired thatsubstantially all of the liquid coolant be withdrawn from the coolingapparatus, for instance, when transitioning to a transport mode of thecooling apparatus or electronic system.

Note that in the embodiment of FIG. 6A, the coolant-carrying compartment420 includes multiple thermally conductive fins 421 extending upwardsfrom base surface 425, and disposed between coolant inlet manifoldregion 422 and coolant outlet manifold region 423. As noted above, thethermally conductive fins 421 are disposed within coolant-carryingcompartment 420 to facilitate heat transfer from the heat sink to theliquid coolant flowing through the coolant-carrying compartment, and maycomprise various configurations, including pin fins or plate fins, andif desired, coolant flow channels of varying cross-section, to furtherenhance heat transfer. In the illustrated embodiment, coolant outlettube 600 extends into the coolant outlet manifold region 423, close tobase surface 425 of coolant-carrying compartment 420. For instance, thecoolant outlet tube 600 may extend into the coolant-carrying compartment420 to a lower portion or lower half of the multiple thermallyconductive fins 421, as illustrated. Thus, coolant outlet tube 600extends into coolant-carrying compartment 420 to a lower region of thecoolant-carrying compartment itself. Therefore, upon draining thecooling apparatus using, for instance, a coolant-serving apparatus suchas described above in connection with FIG. 5, more liquid coolant willadvantageously be removed from coolant-carrying compartment 420 ofliquid-cooled heat sink 400′ since the outlet tube is lower within thecoolant-carrying compartment.

FIG. 6B depicts an alternate embodiment of a liquid-cooled heat sink400″ analogous to liquid-cooled heat sink 400′ described above inconnection with FIG. 6A, except that in this embodiment, the coolantoutlet tube 601 extends down to meet (or approximately meet) basesurface 425 of coolant-carrying compartment 420. Further, the heat sinkincludes a recess 602 aligned below coolant outlet tube 601 and sizedand configured to facilitate liquid coolant flow into the opening orchannel of coolant outlet tube 601 from coolant-carrying compartment420. Note in this embodiment, coolant outlet tube 601 could extend tojust short of base surface 425 of coolant-carrying compartment 420, oreven extend slightly into recess 602, depending on the size of therecess and size of the coolant outlet tube 601. The balance beingdisclosed herein is between ensuring better removal of coolant from ahorizontally-disposed, liquid-cooled heat sink, while not significantlyaffecting pressure drop of coolant flow through the heat sink in normaloperation.

FIG. 6C depicts a further variation, wherein a liquid-cooled heat sink400′″ is provided which includes a coolant outlet tube 601 that againextends into the coolant-carrying compartment 420, and in this case,through the coolant outlet manifold region 423 to contact (or almostcontact) base surface 425 of coolant-carrying compartment 420. One ormore openings 603 are provided in a sidewall of the coolant outlet tube601 to facilitate coolant drainage from the coolant-carrying compartmentthrough the coolant outlet tube 601. Note that the one or more openings603 in the sidewall of the coolant outlet tube 601 are located in alower region of the coolant-carrying compartment 420 of the thermallyconductive structure 415 to facilitate enhanced drainage of liquidcoolant from the coolant-carrying compartment when transitioning thecooling apparatus from, for instance, an operational mode to a transportmode, where most, if not all, of the liquid coolant is to be removedfrom the cooling apparatus.

Note that if desired, the embodiments of FIGS. 6B & 6C could becombined, with a recess being provided in the thermally conductivestructure aligned below the coolant outlet tube 601 illustrated in FIG.6C to, for instance, provide further coolant flow through the heat sinkvia the coolant outlet tube.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise” (andany form of comprise, such as “comprises” and “comprising”), “have” (andany form of have, such as “has” and “having”), “include” (and any formof include, such as “includes” and “including”), and “contain” (and anyform contain, such as “contains” and “containing”) are open-endedlinking verbs. As a result, a method or device that “comprises”, “has”,“includes” or “contains” one or more steps or elements possesses thoseone or more steps or elements, but is not limited to possessing onlythose one or more steps or elements. Likewise, a step of a method or anelement of a device that “comprises”, “has”, “includes” or “contains”one or more features possesses those one or more features, but is notlimited to possessing only those one or more features. Furthermore, adevice or structure that is configured in a certain way is configured inat least that way, but may also be configured in ways that are notlisted.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.

What is claimed is:
 1. A cooling apparatus comprising: a liquid-cooledheat sink, the liquid-cooled heat sink comprising: a thermallyconductive structure configured to couple along a horizontal main heattransfer surface thereof to at least one electronic component to becooled, the thermally conductive structure comprising a coolant-carryingcompartment through which liquid coolant flows, at least in part, in adirection substantially parallel to the horizontal main heat transfersurface of the thermally conductive structure; a coolant inlet tube anda coolant outlet tube associated with the thermally conductive structureand in fluid communication with the coolant-carrying compartment of thethermally conductive structure to facilitate the liquid coolant flowtherethrough; and wherein the coolant-carrying compartment of thethermally conductive structure comprises a base surface, and the coolantoutlet tube extends into the coolant-carrying compartment towards thebase surface thereof to facilitate withdrawal of the liquid coolanttherefrom for a transport mode of the cooling apparatus.
 2. The coolingapparatus of claim 1, wherein the thermally conductive structureincludes multiple thermally conductive fins within the coolant-carryingcompartment, and the coolant outlet tube extends into thecoolant-carrying compartment to a lower portion of the multiplethermally conductive fins.
 3. The cooling apparatus of claim 1, whereinthe coolant outlet tube extends into the coolant-carrying compartment toa lower region of the coolant-carrying compartment.
 4. The coolingapparatus of claim 1, wherein the coolant outlet tube extends into thecoolant-carrying compartment to the base surface of the coolant-carryingcompartment, and the base surface of the coolant-carrying compartmentincludes a recess aligned below the coolant outlet tube to facilitateliquid coolant flow into the coolant outlet tube from thecoolant-carrying compartment.
 5. The cooling apparatus of claim 4,wherein the thermally conductive structure further includes: multiplethermally conductive fins within the coolant-carrying compartment; and acoolant inlet manifold region and a coolant outlet manifold regionwithin the coolant-carrying compartment, the coolant inlet manifoldregion receiving coolant from the coolant inlet tube, and the coolantoutlet manifold region exhausting coolant through the coolant outlettube, the multiple thermally conductive fins within the coolant-carryingcompartment being disposed, at least in part, between the coolant inletmanifold region and the coolant outlet manifold region thereof, and thecoolant outlet tube extending into the coolant outlet manifold region ofthe coolant-carrying compartment.
 6. The cooling apparatus of claim 1,wherein the coolant outlet tube extends into the coolant-carryingcompartment to the base surface of the coolant-carrying compartment, andthe coolant outlet tube includes at least one opening in a sidewallthereof which facilitates coolant drainage from the coolant-carryingcompartment through the coolant outlet tube.
 7. The cooling apparatus ofclaim 6, wherein the at least one opening in the sidewall of the coolantoutlet tube is located in a lower region of the coolant-carryingcompartment of the thermally conductive structure.
 8. The coolingapparatus of claim 7, wherein the thermally conductive structure furtherincludes: multiple thermally conductive fins within the coolant-carryingcompartment; and a coolant inlet manifold region and a coolant outletmanifold region within the coolant-carrying compartment, the coolantinlet manifold region receiving coolant from the coolant inlet tube, andthe coolant outlet manifold region exhausting coolant through thecoolant outlet tube, the multiple thermally conductive fins within thecoolant-carrying compartment being disposed, at least in part, betweenthe coolant inlet manifold region and the coolant outlet manifold regionthereof, and the coolant outlet tube extending into the coolant outletmanifold region of the coolant-carrying compartment.
 9. The coolingapparatus of claim 1, wherein the thermally conductive structure furthercomprises a coolant inlet manifold region and a coolant outlet manifoldregion within the coolant-carrying compartment, the coolant inletmanifold region receiving coolant from the coolant inlet tube, and thecoolant outlet manifold region exhausting coolant through the coolantoutlet tube, wherein the coolant outlet tube extends into the coolantoutlet manifold region of the coolant-carrying compartment to a lowerregion of the coolant-carrying compartment.
 10. The cooling apparatus ofclaim 1, wherein the thermally conductive structure further includesmultiple thermally conductive fins within the coolant-carryingcompartment, and the coolant outlet tube extends into thecoolant-carrying compartment to a lower portion of the multiplethermally conductive fins.
 11. A cooled electronic module comprising: atleast one electronic component to be cooled; and a cooling apparatus tofacilitate cooling the at least one electronic component, the coolingapparatus comprising: a liquid-cooled heat sink coupled to the at leastone electronic component to be cooled along a horizontal main heattransfer surface thereof, the liquid-cooled heat sink comprising: athermally conductive structure comprising the horizontal main heattransfer surface of the liquid- cooled heat sink, and a coolant-carryingcompartment through which coolant flows, at least in part, in adirection substantially parallel to the main heat transfer surface ofthe liquid-cooled heat sink; a coolant inlet tube and a coolant outlettube associated with the thermally conductive structure and in fluidcommunication with the coolant-carrying compartment of the thermallyconductive structure to facilitate the liquid coolant flow therethrough;and wherein the coolant-carrying compartment of the thermally conductivestructure comprises a base surface, and the coolant outlet tube extendsinto the coolant-carrying compartment towards the base surface thereofto facilitate withdrawal of the liquid coolant therefrom for a transportmode of the cooled electronic module.
 12. The cooled electronic moduleof claim 11, wherein the thermally conductive structure includesmultiple thermally conductive fins within the coolant-carryingcompartment, and the coolant outlet tube extends into thecoolant-carrying compartment to a lower portion of the multiplethermally conductive fins.
 13. The cooled electronic module of claim 11,wherein the coolant outlet tube extends into the coolant-carryingcompartment to a lower region of the coolant-carrying compartment. 14.The cooled electronic module of claim 13, wherein the coolant outlettube extends into the coolant-carrying compartment to the base surfaceof the coolant-carrying compartment, and the base surface of thecoolant-carrying compartment includes a recess aligned below the coolantoutlet tube to facilitate liquid coolant flow into the coolant outlettube from the coolant-carrying compartment.
 15. The cooled electronicmodule of claim 14, wherein the thermally conductive structure furtherincludes: multiple thermally conductive fins within the coolant-carryingcompartment; and a coolant inlet manifold region and a coolant outletmanifold region within the coolant-carrying compartment, the coolantinlet manifold region receiving coolant from the coolant inlet tube, andthe coolant outlet manifold region exhausting coolant through thecoolant outlet tube, the multiple thermally conductive fins within thecoolant-carrying compartment being disposed, at least in part, betweenthe coolant inlet manifold region and the coolant outlet manifold regionthereof, and the coolant outlet tube extending into the coolant outletmanifold region of the coolant-carrying compartment.
 16. The cooledelectronic module of claim 11, wherein the coolant outlet tube extendsinto the coolant-carrying compartment to the base surface of thecoolant-carrying compartment, and the coolant outlet tube includes atleast one opening in a sidewall thereof which facilitates liquid coolantdrainage from the coolant-carrying compartment through the coolantoutlet tube.
 17. The cooled electronic module of claim 16, wherein theat least one opening in the sidewall of the coolant outlet tube islocated in a lower region of the coolant-carrying compartment of thethermally conductive structure.
 18. The cooled electronic module ofclaim 17, wherein the thermally conductive structure further includes:multiple thermally conductive fins within the coolant-carryingcompartment; and a coolant inlet manifold region and a coolant outletmanifold region within the coolant-carrying compartment, the coolantinlet manifold region receiving coolant from the coolant inlet tube, andthe coolant outlet manifold region exhausting coolant through thecoolant outlet tube, the multiple thermally conductive fins within thecoolant-carrying compartment being disposed, at least in part, betweenthe coolant inlet manifold region and the coolant outlet manifold regionthereof, and the coolant outlet tube extending into the coolant outletmanifold region of the coolant-carrying compartment.
 19. The cooledelectronic module of claim 11, wherein the thermally conductivestructure further comprises a coolant inlet manifold region and acoolant outlet manifold region within the coolant-carrying compartment,the coolant inlet manifold region receiving coolant from the coolantinlet tube, and the coolant outlet manifold region exhausting coolantthrough the coolant outlet tube, wherein the coolant outlet tube extendsinto the coolant outlet manifold region of the coolant-carryingcompartment to a lower region of the coolant-carrying compartment.
 20. Amethod comprising: providing a cooling apparatus comprising aliquid-cooled heat sink configured to facilitate cooling at least oneelectronic component, the cooling apparatus comprising an operationalmode and a transport mode, the liquid-cooled heat sink comprising: athermally conductive structure configured to couple along a horizontalmain heat transfer surface thereof to the at least one electroniccomponent to be cooled, the thermally conductive structure comprising acoolant-carrying compartment through which liquid coolant flows, atleast in part, in a direction substantially parallel to the horizontalmain heat transfer surface of the thermally conductive structure; acoolant inlet tube and a coolant outlet tube associated with thethermally conductive structure and in fluid communication with thecoolant-carrying compartment of the thermally conductive structure tofacilitate the liquid coolant flow therethrough; and wherein thecoolant-carrying compartment of the thermally conductive structurecomprises a base surface, and the coolant outlet tube extends into thecoolant-carrying compartment towards the base surface thereof tofacilitate withdrawal of the liquid coolant therefrom in the transportmode of the cooling apparatus.